The invention relates to apparatus for magnetically securing one object to another and, more particularly, to an apparatus intended for magnetic securement to an object and having extremely high intrinsic lateral adherence thereto.
It has hitherto not been known to make effective economical use of relatively low power magnets for the purpose of securing relatively heavy objects against steel or other ferromagnetic, or paramagnetic, surfaces so as effectively to resist lateral movement across such surfaces. To preclude apparatus from being moved laterally across the surface, it has been conventional to employ relatively high magnetic forces or to use the combination of magnetic forces and permanent adhesives in combination to effect a non-releasable adherence of one object to another.
It is a common procedure to utilize small permanent magnets for the securement of paper or the like to steel surfaces. Yet, it has not been practical to magnetically secure a heavy display board or the like to a steel or other ferromagnetic or paramagnetic surface because of the expense, weight and sheer bulk of permanent magnets required to develop sufficient forces of magnetic attraction to cause an item to be maintained in position by the magnet, to remain in position on such surface even though there may be high forces tending to laterally displace the same.
While it is, of course, an old and well known expedient to secure a magnet to an object for the purpose of attaching that object to another object, it is, however, almost invariably characteristic of small permanent magnets which typically are of such materials as plastic, ceramic, or alloyed metals (e.g. alnico), that the magnet material characteristically is so hard or slippery that the ratio of a force necessary to displace the magnet laterally across a surface, such as smooth enameled or polished steel or other ferromagnetic material, is typically so low in relationship to the pull force of the magnet as to effectively preclude the application of a usefully high lateral force to the magnet. Typically, the lateral force required to displace a low power magnet from a surface to which it is magnetically attached, is far less than the magnetic pull force. For example, for most small or low power plastic, ceramic or metallic magnets of relatively low power which are commercially obtainable, the displacement force may typically be only 20% to 30% of the pull force of the magnet.
In other words, such plastic, polymer based ceramic or metal magnets of the type noted usually can be displaced by relatively small forces tangential to the surface (i.e., displacement force) upon which they are applied when that surface is a typically smooth one such as bare, painted, enameled or other treated metal.
Although it is possible, of course, to provide magnets and the surfaces to which they are to be attached with interlocking grooves or the like, or to provide a permanent adhesive between the magnet and surface as disclosed in Fayling U.S. Pat. No. 3,897,288, more frequently such expedients are undesirable or impossible and it is instead desired to effect adhesion of a magnetic apparatus to a ferrous metal surface or to any other object having a ferromagnetic or paramagnetic material by the use of a magnet of sufficient strength to cause the magnet to adhere to the surface by the simple expedient of static friction. The prior art is replete with numerous structures and apparatus having magnets which are applied directly to the surface to which the magnet will provide magnetic attraction.
On the other hand, it has been known to imbed or recess magnets within a non-magnetic material of a resilient nature, such as rubber, for the purpose of causing the material to contact the surface to which the magnets are attracted. Such structures are taught, for example, in U.S. Pat. Nos. 2,621,661; 2,666,352; and 2,709,245. In each of these patents, a relatively small, light article is adapted for being secured to a ferrous metal surface by a magnet which is positioned in rubber material so that only rubber is in contact with the ferrous surface. While magnets can be employed in this fashion to provide sufficient forces of magnetic attraction and adhesion to a surface to which the magnet is attracted to cause the article to remain in position if it is of sufficiently light weight, as a practical matter, such structures of magnets imbedded in rubber or similar materials do not provide sufficiently high intrinsic lateral adherence to the surface to which the magnet is attracted if the article has a weight which begins to approach the bare pull force of the magnet.
It has been known to concurrently apply magnetic forces and adhesive forces to fasten articles together. A method of doing so is disclosed in Fayling U.S. Pat. No. 3,897,288 wherein layers of reactive adhesive are carried on exterior bonding faces of a magnetized polymer-based article. The polymer-based magnet is placed between adjacent articles during a fastening operation to apply a magnetic force tending to draw the articles together and to apply pressure on the adhesive material disposed between the articles. Hence, the magnetic forces between the articles tend to cause the structure to be stably maintained until the adhesive can be set. However, the method disclosed in said Fayling patent precludes removing a magnetically secured article after the adhesive has become set. Hence, the arrangement is not releasably adhesive as is desired in many situations in which an article to be magnetically secured to a surface so that the article can be readily removed and relocated to another position on the surface. There are numerous other teachings in the prior art of arrangement in which magnetic structures are permanently adhered by a non-releasable adhesive to a surface. For example, such arrangements are disclosed in U.S. Pat. Nos. 3,195,022 and 3,365,684.
A need which is frequently encountered domestically illustrates the desirability of providing a display structure which is removably secured to a surface and yet may stably be maintained on such surface by forces of magnetic attraction. In many busy households, particularly with families having children, it is common practice to secure various sheets of paper, loose leaves, clippings, coupons, memos and shopping lists to the front of a refrigerator or other ferrous metal appliance by the use of small permanent magnets. Such an arrangement is not only unsightly but remarkably ineffective since the magnets typically will not support much weight. It is, therefore, nut uncommon for such items to slide down or fall off the front face of the appliance. In addition, such arrangements do not permit the magnetic securement of a pad of memos or shopping lists to the front face of the appliance since such pads are too heavy to be supported by small permanent magnets.
Accordingly, there is a need for a display device which can be magnetically secured to the upright surface of a refrigerator or similar appliance which is capable of supporting a pad or numerous sheets of such items as sheets of paper, clippings, coupons, memos or shopping lists. Of course, sufficient hang force for supporting noteboards, memo pad holders, and the like, may be obtained by using strong, metal button magnets or large surfaced plastic flexible magnetic sheets or strips where such magnets are applied directly to the surface of the appliance. In such case, the static friction which is sufficient to prevent such apparatus from being displaced laterally on the surface, such as by force of gravity, will, in any event, be provided by the rough metal surface irregularities of such magnet which dig into the ferrous metal face, or painted or other treated surface, of the appliance. This result is totally unacceptable since the surface will be scratched upon not only any application of the magnet but any sliding thereof. In any event, such strong, metal button magnets are relatively expensive.
Various attempts have been made in the past to overcome the problem of applying magnets directly to ferrous or painted ferrous metal surfaces. For example, Rice U.S. Pat. No. 3,230,653 discloses a license plate holder having a bracket to which are secured flat elongated magnetic members which are constructed of flexible resilient permanent magnetic material. Of course, such material is well known in the market place but typically is incapable of providing high static friction to the surface to which it is applied and, hence, is most readily displaced laterally by gravity or other forces acting tangentially to the surface to which the magnet is secured.
Similarly, Podoloff U.S. Pat. No. 3,245,165 discloses an arrangement for mounting signs or the like to a ferrous support, such as on the side of a vehicle. For this purpose, there is disclosed in the latter patent a device comprising an annular magnet which is retained by a resilient rubber sleeve of annular shape. The sleeve extends under the magnet so as to provide a surface for bearing against the ferrous metal support to which the magnet provides a magnetic attraction. This precludes marring of the surface. However, it has been found that rubber of such character does not provide sufficient intrinsically high lateral adherence to the surface to support heavy weights unless extremely high power, expensive magnets are utilized.
Moskowitz U.S. Pat. No 3,082,982 also discloses an arrangement in which magnets are utilized to maintain a staff support or the like on the top surface of a vehicle, for example. The arrangement disclosed therein includes a magnet having pole pieces which extend from the structure of the staff support and, to preclude scuffing of the top of the vehicle. The pole pieces are coated with a protective plastic coating. The structure is intended to provide a relatively high co-efficient of friction between the pole pieces and the vehicle body. However, the apparatus disclosed in said Moskowitz Patent is not suited for securement of a memoboard, noteboard, or the like to the vertical, or upright, surface of an appliance and is not such as to provide sufficient lateral adherence to such an upright surface to preclude lateral displacement of the same in response to high forces, such as the gravity acting on the heavy device, which tend to displace the same.
As a matter of generality, magnetic display boards for use in places such as kitchens, on the front or other surfaces of refrigerators, appliances, or cabinets of sheet steel or other ferrous metal, which usually are covered with enamel but are sometimes of a stainless steel construction, and steel cabinets, such as file cabinets or the like in offices, have hitherto not been widely used to hold significant weights. Chiefly, the problems with such prior devices are that they are either too costly to manufacture because of the powerful magnets required and the requisite methods of constructing the same to incorporate such magnets, or have been too lacking in "hang force" to accommodate the holding of significant weights, such as a pad of paper, memos, shopping lists or the like where such pad is more than a few square inches in area and is of useful thickness.
In the case of appliances, the front surface of the same often is typically not a plane surface, but instead it is often slightly curved about a vertical axis or may be, in fact, a convex surface or irregular surface. Consequently, the securement of a display device to such surface presents the problem that, if the magnets affixing the same to such surface cannot be adjusted, they will tend to be held out away from the surface except at one point of contact or, at best, one line of contact. Only magnets at that point of contact, or along such line of contact, will provide effective forces of magnetic attraction to such surface since, as is known, the attractive forces of a magnet to such surface fall off abruptly with any spacing of the magnet from the surface. Consequently, if the magnet is not close to the surface its attractive power is greatly diminished. This can be overcome by an adjusting mechanism for enabling each of a plurality of magnets of such a device to contact such surface, but any adjusting mechanism desirably must avoid adding any excessive weight to the device and should not unnecessarily increase the distance of the device from the surface to which it is to be magnetically secured in order to preclude undesirable displacement of the center of gravity and, therefore, undesirable leverage of such device away from the surface to which it is to be secured, to prevent "peeling away".
In this regard, it is desirable that the center of gravity of the display apparatus affixed by magnets to an adjacent surface be placed as close as possible to the surface. As the center of gravity is displaced further outward from the surface to which the apparatus is secured, a greater moment of force is created by gravity which moment tends to detach the apparatus from such surface.
Consequently, a memo board for magnetic securement to a vertical surface must desirably overcome these difficulties if it is to remain in place for serving its intended purpose. Additionally, however, such display apparatus must have a sufficient margin of weight-carrying ability that it will remain in place even though jarred, shaken, jolted or otherwise disturbed so as to avoid the possibility of becoming dislodged and thus falling with a danger of injury to a person such as a young child opening or closing a refrigerator door to which the apparatus is attached.